1. Field of the Invention
The present invention relates to a dielectric ceramic and a laminated ceramic capacitor, and more particularly, relates to the microstructure of a dielectric ceramic which is suitable for use in a thin-layer high-capacity laminated ceramic capacitor, and a laminated ceramic capacitor configured with the use of the dielectric ceramic.
2. Description of the Related Art
As one of the effective measures for satisfying the needs of reduction in size and increase in capacity for laminated ceramic capacitors, the reduction in thickness is conceived for dielectric ceramic layers provided in the laminated ceramic capacitors. Therefore, the dielectric ceramic layers may be made thinner to a thickness, for example, on the order of 1 μm. However, as the dielectric ceramic layers are further reduced in thickness, the electric field applied per dielectric ceramic layer is relatively higher. Therefore, the improvement in reliability in the case of applying a voltage, more specifically, the improvement in lifetime characteristics particularly in a moisture resistance loading test and a high temperature loading test is required for the dielectric ceramic used.
A dielectric ceramic of interest to the present invention is described in, for example, Japanese Patent Application Laid-Open No. 10-330160 (Patent Document 1), which discloses a technique for improving the dielectric breakdown voltage of a dielectric ceramic, and more specifically, discloses the following.
BaCO3 and TiO2 with MnO added thereto are calcined to obtain Ba(Ti, Mn)O3. This calcined Ba(Ti, Mn)O3 with MnO, MgO, Dy2O3, and a Li2O+SiO2+BaO glass component added thereto is calcined to obtain a material for the formation of green sheets, and the green sheets formed from the material are used to form a laminate for a laminated capacitor. The laminate is fired in a reducing atmosphere, and then subjected to an oxidation treatment. This distributes Mn in both a ferroelectric phase section (core) and a paraelectric phase section (shell) of crystal grains in a substantially uniform fashion, thereby increasing the dielectric breakdown voltage.
However, even in the case of using the dielectric ceramic described in Patent Document 1 described above, the further reduction in the thickness of the dielectric ceramic layers leads to insufficient reliability, in particular, insufficient lifetime characteristics in a high temperature loading test and a moisture resistance loading test, and further improvements have been thus desired. It is to be noted that Patent Document 1 fails to disclose the thickness of the dielectric ceramic layers at all.